The present invention relates to a method for the remote identification of mobile labels in an interrogation field, as well as to a corresponding device.
Numerous technical fields now require remote identification of transceivers, each having a particular code permitting a distinction to be made between them. These devices are in principle connected to an object or person whose identification they permit, hence the name labels given to them. Reference can be made to personnel access control through a portico, the control of the passage of animals, the identification of baggage or objects on a conveyor, products or tools on a production line, as well as automatic tolls and sales.
When the labels approach an interrogating device, i.e. are included in its interrogation field, they indicate to it their code, after which various information exchanges known as transactions are possible between the interrogating device and the labels, as a function of the particular application. Normally the labels remain mobile during the transaction, their carrier continuing to move in front of the interrogating device and reference is the made to a xe2x80x9cmoving transactionxe2x80x9d. If other labels then pass through the interrogation field, they can only be interrogated subsequently, so that there is a risk of certain labels never being interrogated and can pass through the interrogation field without having been detected.
Various specific ways of identifying a plurality of active labels in the interrogation field have been envisaged. Thus, the interrogating device can make them recite their code in a fragmentwise manner and inhibit each label, i.e. render it provisionally inactive, when it does not supply a code fragment equal to a requested value. When only one active label remains its transaction can be completed and then the interrogating device returns to the inhibited labels, again renders them active and resumes the recital of their codes, requesting from them other fragment values in order to select a different one of them. Recommencement takes place until all the labels have supplied their code and the respective transactions have been completed. In another interrogation procedure, each of the labels present has an allocated transmission time defined in a random manner or on the basis of a number recorded therein. All the labels transmitting in a specific transmission time can be identified. The other labels are allocated a new transmission time. Identification is finished when all the labels have been able to individually transmit. In both cases the interrogation candidate labels can either be any random label present in the interrogation field or a given label batch present in the interrogation field at the start of the identification sequence. In the latter case, exclusively the labels of said batch are rendered active and interrogated and labels arriving during the identification sequence in the interrogation field will form part of the following batch. Each batch is formed either when the preceding batch has been used up (all its labels having been identified and processed) or after the processing of certain labels of the preceding batch or after a given time period. The labels of the preceding batch which have not been identified and processed must then form part of the new batch.
Certain interrogation algorithms have been proposed for the more rapid decoding of the codes. A proposal has consequently been made to read the codes starting alternately by the most significant bit and the least significant bit. As a result of these measures it is no longer necessary to always prioritize the same labels as a function of the value of their code, but they are only palliatives, because they do not permit a significant increase in the label passage rate through the interrogation field.
The object of the invention is to increase this authorized passage rate without risking detection absences by bringing about a substantial coincidence between the identification order of the labels and the entry order in the interrogation field.
Specifically the labels are provided with a time counter, which is initialized and started up on entering the interrogation field and then always interrogating the label which has spent the longest time in the interrogation field.
The invention consequently relates to a method for the individual identification of labels, each having a particular code, where the labels can pass in group form into an interrogation field of an interrogating device and where the interrogating device reads the code of each of the labels of the group, characterized in that each label of the group undergoes an initialization and starting of a presence time counter on entering the interrogation field, and in that the interrogating device firstly reads the code of the not yet identified label of the group having the longest presence time. It also relates to a device for the individual identification of labels, each provided with a particular code, comprising means for the transmission and reception of signals on an interrogating device and each of the labels, characterized in that the labels incorporate a time counter initialized and started up when it enters the interrogation field of the interrogating device and means for temporarily saving the presence times.
This method can be grafted onto all conventional procedures for the identification of labels or for the reading of the code, and more particularly those referred to hereinbefore.